As used herein, the term ‘dynamic range’ (DR) may relate to a capability of the human psychovisual system (HVS) to perceive a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest darks to brightest brights. In this sense, DR relates to a ‘scene-referred’ intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a ‘display-referred’ intensity. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g. interchangeably.
As used herein, the term high dynamic range (HDR) relates to a DR breadth that spans the some 14-15 orders of magnitude of the human visual system (HVS). For example, well adapted humans with essentially normal (e.g., in one or more of a statistical, biometric or opthamological sense) have an intensity range that spans about 15 orders of magnitude. Adapted humans may perceive dim light sources of as few as a mere handful of photons. Yet, these same humans may perceive the near painfully brilliant intensity of the noonday sun in desert, sea or snow (or even glance into the sun, however briefly to prevent damage). This span though is available to ‘adapted’ humans, e.g., those whose HVS has a time period in which to reset and adjust.
In contrast, the DR over which a human may simultaneously perceive an extensive breadth in intensity range may be somewhat truncated, in relation to HDR. As used herein, the terms ‘visual dynamic range’ or ‘variable dynamic range’ (VDR) may individually or interchangeably relate to the DR that is simultaneously perceivable by a HVS. As used herein, VDR may relate to a DR that spans 5-6 orders of magnitude. Thus while perhaps somewhat narrower in relation to true scene referred HDR, VDR nonetheless represents a wide DR breadth. As used herein, the term ‘simultaneous dynamic range’ may relate to VDR.
Until fairly recently, displays have had a significantly narrower DR than HDR or VDR. Television (TV) and computer monitor apparatus that use typical cathode ray tube (CRT), liquid crystal display (LCD) with constant fluorescent white back lighting or plasma screen technology may be constrained in their DR rendering capability to approximately three orders of magnitude. Such conventional displays thus typify a low dynamic range (LDR), also referred to as a standard dynamic range (SDR), in relation to VDR and HDR.
Advances in their underlying technology however allow more modern display designs to render image and video content with significant improvements in various quality characteristics over the same content, as rendered on less modern displays. For example, more modern display devices may be capable of rendering high definition (HD) content and/or content that may be scaled according to various display capabilities such as an image scaler. Moreover, some more modern displays are capable of rendering content with a DR that is higher than the SDR of conventional displays.
For example, some modern LCD displays have a backlight unit (BLU) that comprises a light emitting diode (LED) array. The LEDs of the BLU array may be modulated separately from modulation of the polarization states of the active LCD elements. This dual modulation approach is extensible (e.g., to N-modulation layers wherein N comprises an integer greater than two), such as with controllable intervening layers between the BLU array and the LCD screen elements. Their LED array based BLUs and dual (or N-) modulation effectively increases the display referred DR of LCD monitors that have such features.
Such “HDR displays” as they are often called (although actually, their capabilities may more closely approximate the range of VDR) and the DR extension of which they are capable, in relation to conventional SDR displays represent a significant advance in the ability to display images, video content and other visual information. The color gamut that such an HDR display may render may also significantly exceed the color gamut of more conventional displays, even to the point of capably rendering a wide color gamut (WCG). Scene related HDR or VDR and WCG image content, such as may be generated by “next generation” movie and TV cameras, may now be more faithfully and effectively displayed with the “HDR” displays (hereinafter referred to as ‘HDR displays’).
As with the scalable video coding and HDTV technologies, extending image DR typically involves a bifurcate approach. For example, scene referred HDR content that is captured with a modern HDR capable camera may be used to generate an SDR or a VDR version of the content, which may be displayed on VDR displays or conventional SDR displays. In one approach, as described in U.S. provisional application 61/476,174 “Improved encoding, decoding, and representing high dynamic range images,” by W. Jia et al., herein incorporated by reference for all purposes, the SDR version is generated from the captured VDR version by applying a tone mapping operator (TMO) to intensity (e.g., luminance, luma) related pixel values in the HDR content. The Jia application also describes how an HDR image can be represented by a baseline SDR image, a ratio image, and a chroma residual.
The “Digital Cinema Systems Specification,” Version 1.2, Mar. 7, 2008, by Digital Cinema Initiatives, LLC, is referred to herein as the DCI System Specification, or simply as DCI, defines the technical specifications and requirements for the mastering, coding, and distribution of digital cinema content. DCI supports video streams at two resolutions: 2K (2048×1080) and 4K (4096×2160). Furthermore, DCI images are coded as 12-bit, X′Y′Z′ color channels, using the JPEG 2000 coding standard. This representation is inadequate to fully represent HDR content. Embodiments of this invention describe methods for the mastering, coding, and distribution of HDR content in formats that are backwards compatible with the existing DCI specification. As used herein, “JPEG-2000” refers to the JPEG-2000 compressor/decompressor (codec) standard of the Joint Motion Picture Experts Group (JPEG). As used herein, ‘TIFF’ refers to a Tagged Image File Format.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.